What size notched trowel should I use to install Schluter™-KERDI?

A 1/4" x 3/16" (6 mm x 5 mm) V-notched trowel or the Schluter™-KERDI-TROWEL is recommended. Mix the Schluter SET™ , ALL-SET™ , FAST-SET™, or unmodified thin-set mortar to a fairly fluid consistency (but still able to hold a notch) and solidly embed the KERDI into the fresh mortar with the flat side of the trowel (a drywall knife is handy for this purpose as well). Periodically lift a corner of the KERDI after embedding it in the thin-set mortar to check the fleece for full coverage.